To be honest, Congo Natty never really made what most people consider "ragga." X-Project came the closest of the CN offshoots, but even then it wasn't much.

One important thing to consider is what does your friend consider ragga? Is he more into the earlier styles, like around '93, or when ragga was becoming quite predictable, around '95? Also, is he just interested in ragga, or is he also into oldskool and hardcore?